Biodiversity is generated through the formation of new species. In several organisms, especially butterflies, differences among species are often due to genes on the X chromosome, the chromosome which is responsible for determining gender. Genes on the X chromosome may evolve faster than autosomal genes, which could explain why the X chromosome plays such a large role in the differentiation of species. Faster evolution of X-linked genes, or 'fast X' evolution, can be identified by comparing the number of DNA sequence changes between two species in genes located on the X chromosome compared to the other chromosomes, the autosomes. To test this hypothesis, DNA sequence will be analyzed from both X-linked and autosomal genes in the clouded and orange sulphur butterflies (Colias philodice and C. eurytheme, respectively). Several traits that distinguish these butterflies, such as wing pigmentation, mate selection, and fertility, have been genetically mapped to the X chromosome, providing a "best case" system to test the fast X evolution hypothesis.
Modern evolutionary biologists have an impressive understanding of how genes evolve within populations, but a poorer understanding of the genetics underlying divergence among species. This research will illuminate the genetic basis of speciation, providing insights into the fundamental evolutionary processes that regulate biodiversity on Earth. It will also offer insight into genetic attributes that allow different species to persist together, which has become increasingly important when human activities threaten the extinction of many species.
